1. Technical Field
The present invention relates to signal modulations in general, and in particular to an apparatus for controlling signal modulations. Still more particularly, the present invention relates to an apparatus for controlling modulation of an alternating waveform on a direct current voltage signal within a low-noise block controller.
2. Description of Related Art
A digital satellite communication system typically employs a ground-based transmitter that beams an uplink signal to a satellite positioned in a geosynchronous orbit. In turn, the satellite relays the signal back to various ground-based receivers. Such digital satellite communication system permits a household (or business) subscribing a satellite television service to receive audio and video signals directly from the satellite by means of a directional receiver antenna that is typically affixed to the roof or an external wall of the subscriber's residence.
A directional receiver antenna constructed to receive satellite signals typically includes a dish-shaped reflector that has a feed support arm protruding outward from the front surface of the reflector. The feed support arm supports an assembly in the form of a low-noise block (LNB) amplifier having an integrated LNB feed. The reflector collects and focuses satellite signals onto the LNB feed.
The satellite signals are commonly received at the Ku-band or C-band. The received satellite signals are first amplified and then downshifted to a predetermined frequency band, typically in the L-band. The satellite signals are then sent via a coaxial cable to a set-top box typically located adjacent to a subscriber's television.
The components within a set-top box can be divided into two major sections, namely, an LNB control section and a signal processing section. The signal processing section is beyond the scope of the present disclosure. The LNB control section controls the functionality of an LNB amplifier located on the feed support arm of a directional receiver antenna.
Generally speaking, the LNB control section includes, inter alia, a direct current (DC) power supply, a summing circuit, a switch and an LNB control device. The DC power supply, the summing circuit and the switch are discrete components external to the LNB control device. The LNB control device typically generates various control signals for controlling the DC power supply, the summing circuit, and the switch. For example, the LNB control device provides an alternating waveform to be added to a DC voltage signal originated from the DC power supply, and the waveform modulation is performed within the summing circuit. In addition, the LNB control device provides a switch control signal to control the switch that allows the modulated DC voltage signal to pass to an LNB amplifier.
The present disclosure provides an improved apparatus for controlling the modulation of an alternating waveform on a DC voltage signal within a LNB controller.